Lateral position detection and control for friction stir systems

ABSTRACT

A friction stir system for processing at least a first workpiece includes a spindle actuator coupled to a rotary tool comprising a rotating member for contacting and processing the first workpiece. A detection system is provided for obtaining information related to a lateral alignment of the rotating member. The detection system comprises at least one sensor for measuring a force experienced by the rotary tool or a parameter related to the force experienced by the rotary tool during processing, wherein the sensor provides sensor signals. A signal processing system is coupled to receive and analyze the sensor signals and determine a lateral alignment of the rotating member relative to a selected lateral position, a selected path, or a direction to decrease a lateral distance relative to the selected lateral position or selected path. In one embodiment, the friction stir system can be embodied as a closed loop tracking system, such as a robot-based tracked friction stir welding (FSW) or friction stir processing (FSP) system.

RELATED APPLICATIONS

This application is a divisional application of, and claims priority toU.S. Ser. No. 12/130,622, filed May 30, 2008, contents which areincorporated by reference herein.

GOVERNMENT RIGHTS

The United States Government has certain rights in embodiments of thepresent invention pursuant to prime contract No. W-7405-ENG-36 with theUnited States Department of Energy.

FIELD OF THE INVENTION

The present invention relates to friction stir systems (FSS) includingfriction stir welding (FSW) and friction stir processing (FSP) systems,and related position detection methodologies for such systems.

BACKGROUND

One FSS embodiment is FSW. FSW is a joining process where welding isaccomplished via mechanical stirring at a temperature that is below themelting point of the material being welded. In FSW, the welding toolcomprises a shoulder and a pin (also called a probe). The tool isrotated while traversing the weld line. The shoulder applies pressureand friction induced heat to the surface of the material while the probeplunges into the material and induces material flow.

Another FSS embodiment is referred to as friction stir processing (FSP).FSP is a surface treatment technique which generally uses the same toolbody as FSW, but lacks a FSW type probe. FSP is a relatively newsurface-engineering technology that can locally eliminate or reducecasting defects and refine microstructures, thus improving strength andductility, increasing resistance to corrosion and fatigue, enhancingformability, and improving other properties. FSP can also producefine-grained microstructures through the thickness, imparted bysuperplasticity. Analogous to FSW, in FSP there is generally substantialand complex material flow.

FSW can be applied in a number of configurations, or positions, of thematerial to be welded and the FSW tool. One FSW configuration isreferred to as butt-weld. In this arrangement the materials to bejointed are generally butted together side by side. The tool traversesthe seam between the two samples, welding them together. The probegenerally extends nearly to the base of the material. In this case, itis desirable for the probe to be well positioned with respect to theweld line.

Another FSW configuration is referred to as lap weld. In this case, thetwo samples are laid one on top of the other. The FSW probe extendsthrough the top material and some distance into the second to accomplishthe weld. Another FSW configuration is referred to as T-joint. In theT-joint, the materials to be welded are arranged in a T, with ahorizontally-oriented sample set on top of a vertically-oriented sample.Other FSW configurations include the corner weld and edge weld.

As known in the art, welds from FSW can experience a loss in weldquality when the system parameters and conditions are not well set. Forinstance, in the case of FSW, loss of quality can occur if the weldingtool rotates too slowly, or too quickly, or if the probe is not thecorrect length for the material (e.g. a probe in butt-welding extendsonly halfway through the material, leaving the lower half of the seamun-bonded).

One flaw-inducing condition for FSW and FSP systems can be due tolateral misalignment during the FSW or FSP process. Lateral misalignmentresults when the FSW or FSP tool is offset relative to the selectedlateral position or selected path referenced to the workpiece(s). InFSW, lateral misalignment can cause poor quality welds. In FSP, lateralmisalignment can cause unintended microstructural results.

In the case of FSW, examples of lateral misalignment for lap weld,T-weld and butt weld (left to right) are shown in FIG. 1 as A, B and C,respectively. In lap-welding, lateral misalignment can arise when theprobe is located entirely within the material but the shoulder of thetool is not completely in contact with the upper material. Thiscondition can result in a number of generally undesirable consequencesthat result from insufficient heat input due to less shoulder contactand thus less friction. Also material could be ejected out into the areaunder the exposed shoulder. In the T-joint (FIG. 1B), the probe is shownoffset to the point where a portion of the probe does not reside in thelower material. In T-joints, the geometry of the material beneath theshoulder is changing with lateral offset, in that the tool is more orless centered over the vertical member. Additionally, the probe movestoward or away from the edges of the vertical member. These changingconditions will cause changes in weld quality. Lateral offset is knownto cause deterioration of quality for T-joints in both the extendedun-bonded region to the right of the probe as well as the loss of thematerial which is generally ejected to the left of the probe. Finally inthe butt-joint (FIG. 1C), the probe is shown laterally offset relativeto the joint line sufficiently so that the probe is only in one of thematerial pieces. In butt-joints, the composition of the material underthe shoulder does not change, but the amount the probe is in eachmaterial does. At centered locations, the probe is half in one materialand half in another. In an offset position, it is largely in one piece,and only slightly in the other. The resulting weld quality forsignificant lateral offset in butt-joints will likely be quite low.

Visualization is one known technique for identifying and correctinglateral misalignment. In butt-joint and in some lap weldingconfigurations the alignment of the FSW tool with regard to the weldseam can generally be visually observed. However, in other lap weldsincluding blind T-joint, visualization is not generally possible. Inblind T-joints this inability results because the lower vertical membercannot be seen through the upper horizontal member. Similarly, incertain FSP processes, visualization is not generally possible. There isthus a need for a new technique to better maintain FSW and FSPprocessing tools in a desired lateral alignment during system operation.

SUMMARY

This Summary is provided to comply with 37 C.F.R. §1.73, requiring asummary of the invention briefly indicating the nature and substance ofthe invention. It is submitted with the understanding that it will notbe used to interpret or limit the scope or meaning of the claims.

A friction stir system for processing at least a first workpiececomprises a spindle actuator coupled to a rotary tool comprising arotating member for contacting and processing the first workpiece. Adetection system is provided for obtaining information related to alateral alignment of the rotating member. The detection system comprisesat least one sensor for measuring a force experienced by the rotary toolor a parameter related to the force experienced by the rotary toolduring processing, wherein the sensor provides sensor signals. A signalprocessing system is coupled to receive and analyze the sensor signalsand determine a lateral alignment of the rotating member relative to aselected lateral position, a selected path, or a direction to decrease alateral distance relative to the selected lateral position or selectedpath. In one embodiment, the friction stir system can be embodied as aclosed loop tracking system, such as a robot-based tracked friction stirwelding or friction stir processing system.

FIGURES

FIG. 1A-C shows depictions of laterally misaligned friction stir welding(FSW) probes during a lap weld, T-weld and butt weld, respectively.

FIG. 2A shows a classification tree according to an embodiment of theinvention for a friction stir system configuration havingworkpiece-based lateral position detection including an enhanced and anon-enhanced branch, and exemplary material, surface features, rootfeatures, and thickness variation for the enhanced branch.

FIG. 2B shows specific exemplary workpiece-based enhancement species fora blind T-Joint FSW configuration.

FIG. 2C shows specific exemplary workpiece-based enhancement speciesaccording to an embodiment of the invention for a butt-joint FSWconfiguration.

FIG. 2D shows a classification tree according to an embodiment of theinvention for a friction stir system configuration havingmachine/fixturing-based lateral position detection including an enhancedand a non-enhanced branch, and exemplary backing plate, top clamps, andgap introduction and species thereof that can be used for the signalenhancement branch.

FIG. 2E shows specific exemplary machine/fixturing-based enhancementspecies according to an embodiment of the invention for a blind T-JointFSW configuration.

FIG. 2F shows specific exemplary machine/fixturing-based enhancementspecies according to an embodiment of the invention for a butt-joint FSWconfiguration.

FIG. 3A is a simplified depiction of an exemplary FSS system havinglateral position detection according to an embodiment of the inventionfor processing at least a first workpiece.

FIG. 3B is a simplified depiction of an exemplary FSW system havinglateral position detection according to an embodiment of the invention.

FIG. 4 shows an exemplary friction stir system having through the toollateral position tracking according to an embodiment of the invention.

FIG. 5 shows values for the axial forces experienced by an FSW tool vs.varying amounts of lateral offset, according to an embodiment of theinvention.

FIG. 6 shows the measured x-axis forces experienced by an FSW toolexperienced during welding, according to an embodiment of the invention.

DETAILED DESCRIPTION

The present invention is described with reference to the attachedfigures, wherein like reference numerals are used throughout the figuresto designate similar or equivalent elements. The figures are not drawnto scale and they are provided merely to illustrate the instantinvention. Several aspects of the invention are described below withreference to example applications for illustration. It should beunderstood that numerous specific details, relationships, and methodsare set forth to provide a full understanding of the invention. Onehaving ordinary skill in the relevant art, however, will readilyrecognize that the invention can be practiced without one or more of thespecific details or with other methods. In other instances, well-knownstructures or operations are not shown in detail to avoid obscuring theinvention. The present invention is not limited by the illustratedordering of acts or events, as some acts may occur in different ordersand/or concurrently with other acts or events. Furthermore, not allillustrated acts or events are required to implement a methodology inaccordance with the present invention.

The present Inventors have discovered that the lateral alignment forfriction stir systems (FSS) comprising a rotary tool including arotating member can be automatically detected, and optionally quantifiedand/or tracked by the inclusion of a lateral position detection system.The lateral position detection system measures one or more forcesexperienced by the rotary tool or a parameter related to the force (e.g.vibration via vibration sensing) experienced by the rotary tool duringprocessing. The lateral alignment is generally based on the location ofthe rotating member relative to a selected lateral position or pathreferenced to a first and a second workpiece (e.g. a joint for FSW).

At least one sensor is operable to measure a force experienced by therotary tool or a parameter related to the force experienced by therotary tool during processing, wherein the sensor provides sensorsignals. A signal processing system is coupled to receive and analyzethe sensor signals. The signal processing system can automaticallydetermine the lateral alignment of the rotating member relative to theselected lateral position or selected path, or in the case of theweaving methodology described below, a direction to decrease the lateraldistance to the selected lateral position or selected path.

Although embodiments of the present invention are generally describedrelative to FSW, as will be clear to one having ordinary skill in theart, embodiments of the present invention can be applied to related FSP.As described above, other than the absence of a probe, The FSP systemand method is otherwise generally identical to FSW and embodiments ofthe present invention can be applied in an analogous fashion to FSP.Although the deformation in FSP is generally confined to the workpiecesurface, the process forces have been identified by the presentInventors to generally remain sufficiently high for detection thereof.

Automated lateral misalignment detection and optionally lateralalignment tracking systems according to embodiments of the invention canbe configured for FSS including robotic based FSS. In a typicalembodiment, the force is sensed directly by affixing a force sensor tothe shaft of the FSS tool or below the anvil supporting theworkpiece(s). In this embodiment, the force sensor can comprise adynamometer, strain gauge, pressure sensor, load cell or other suitablesensor. Additionally, signals generated which can give information aboutthe force(s) can generally be used, such as vibration signals.Accordingly, vibration sensors for sensing the vibration of the rotatingmember can also generally be used.

In a typical application, a FSS according to an embodiment of theinvention acquires force signals which it uses to determine lateraloffset. If the signal changes are symmetric about the desired position(e.g. seam) or path, then the system is generally only able to determinethe lateral distance from the desired position, but not direction. Inother cases, the signals obtained are non-symmetric and both thedistance and the lateral direction can generally be obtained. In anotherapplication, an FSS according to an embodiment of the invention can beconfigured to compare the degree of lateral offsets of two locations(without knowing the absolute distance) and obtain the desired lateralposition or path, or information to reduce the lateral distance to thedesired position or path by weaving. Weaving generally comprises movingthe rotating member in the lateral direction (thus orthogonal to thetranslation direction). Weaving is described in more detail below.

Sources of the force or parameter related to force to be sensed by thelateral position detection system can generally be classified as beingworkpiece-based or machine/fixturing based, or a combination of these.Workpiece-based as used herein refers to signals that arise fromcharacteristics of the workpieces being friction stir processed.Machine/fixturing based as used herein refers to signals that arise fromcharacteristics of the FSS itself, such as the clamping, spacers, orfixturing. Both the workpiece-based and machine/fixturing-basedembodiments can also be configured to provide enhanced signals(extrinsic features added) as described below, or operated without anyenhancement (intrinsic or non-enhanced). In the enhanced embodiment, theenhanced signal portion is generally due to features or changes in theworkpiece and/or FSS inserted purposely to induce the enhanced signalportion. In the non-enhanced embodiment, there is no purposeful featuresor change in the workpiece and/or FSS introduced to provide an enhancedsignal portion.

FIG. 2A shows a classification tree 210 according to an embodiment ofthe invention for a FSS configuration having workpiece-based lateralposition detection including an enhanced and a non-enhanced branch. Thenon-enhanced branch can be used, for example, in certain FSWconfigurations, such as lap welding where the two samples overlap onlyin a region (e.g. as shown in FIG. 1A), so that the composition ofmaterial under the shoulder generally changes with lateral position.Lateral offset will thus affect the material composition as the rotatingmember moves across the surface. The change in material compositionresults in a change in the force on the FSW tool that the Inventors havefound can be related to the lateral position of the tool and arelationship established between these parameters.

However, in certain configurations, such as in the lap weld FSWconfiguration where two samples are overlapped completely (or othercases so that generally no offset position has the composition of thematerial under the shoulder change), then the forces will not generallychange with lateral offset because nothing about the material beingstirred or the fixturing is changing with offset. In such cases, anenhanced branch/configuration can be used.

FIG. 2A also shows examples including material, surface features, rootfeatures, and thickness variation that can be used for workpiece-basedsignal enhancement. Some specie categories for the exemplary material,surface features, root features, and thickness variation are also shownin FIG. 2A. FIG. 2B shows some specific exemplary workpiece-basedenhancement species for a blind T-Joint configuration. FIG. 2C showsspecific exemplary sample-based enhancement species for a butt-jointconfiguration.

FIG. 2D shows a classification tree 240 according to an embodiment ofthe invention for a FSS configuration having machine/fixturing-basedlateral position detection having an enhanced and a non-enhanced branch.The non-enhanced configuration can be used when useable signals are dueto system characteristics not purposefully inserted to induce signals.In cases where the non-enhanced version does not provide a satisfactorysignal level, a machine/fixturing branch/configuration can be used toprovide an enhanced signal. FIG. 2D also shows exemplary backing plate,top clamps, and gap introduction that can be used for themachine/fixturing signal enhancement. Some species for the exemplarybacking plate, top clamps, are shown in FIG. 2D.

FIG. 2E shows specific exemplary machine/fixturing-based enhancementspecies for a blind T-Joint configuration. FIG. 2F shows specificexemplary machine/fixturing-based enhancement species for a butt-jointconfiguration. It is noted that some of the exemplary enhancements shownin FIGS. 2A-2F can also be applied to lap welds and butt-joints, or FSP.

FIG. 3A is a simplified depiction of an exemplary FSS system 300 havinglateral position detection according to an embodiment of the inventionfor processing at least a first workpiece 319. The workpiece 319 isshown disposed on supporting anvil 340. System 300 can be embodied forFSW or FSP. FSS tool 305 comprises a spindle actuator 308 having a toolchuck (not shown in FIG. 3A) fixed to a rotating shaft thereof forrotational driving rotary tool 320 comprising rotational member 326including a shoulder for contacting and deforming the workpiece 319.Spindle actuator 308 is generally powered by a motor (e.g. electric) orby a hydraulic. A detection system 310 provides information relating toa lateral alignment of the rotating member 326 relative to a selectedlateral position or selected path referenced to the workpiece 319. Thedetection system 310 comprises at least one sensor 325 operable tomeasure a force experienced by the rotational member 326 or a parameterrelated to the force it experiences during FSW or FSP processing,wherein the sensor 325 provides sensor signals. The sensor 325 shown inFIG. 3A can be a force sensor coupled to the tool 305. In this way,forces experienced by the tool 305 are transmitted through the tool tothe force sensor 325.

Force sensor 310 can comprise a variety of different load cellconfigurations, which as known in the art are electronic transducerswhich convert a force into an electrical signal. This conversion isindirect and can comprise a mechanical arrangement for the force beingsensed deforming a strain gauge, wherein the strain gauge converts thedeformation (strain) to electrical signals. The electrical signal outputis normally on the order of a few millivolts and is generally amplifiedbefore it can be used. The output of the transducer corresponds to theforce applied to the transducer. Although strain gauge load cells arethe most common, hydraulic (or hydrostatic), piezoelectric load cells,and vibrating wire load cells can also generally be used.

In one embodiment, the force sensor 310 comprises a dynamometer. Adynamometer can measure the axial force (Fz), in plane forces Fx and Fy,and the torque around in the axial direction (along the z-axis). Forexample, the dynamometer can comprise a dynamometer provided by KistlerInstrument Corp., Amherst, N.Y., which measures 4 forces: Fx, Fy, Fz andthe Torque around the z-axis.

A signal processing system 315 is coupled to receive and analyze thesensor signals and determine the lateral alignment of the rotatingmember 326 relative to the selected lateral position or selected path,or a direction to decrease a lateral distance to the selected lateralposition or said selected path. Signal processing system 315 cancomprise a microprocessor having associated memory, the memory havingstored correlation information, such as force vs. lateral offsetcorrelation data. In one example, the correlation data shown in FIG. 5or FIG. 6 described in the Examples below can be used.

Although connections for communications between components in FSS 300are generally shown as wired (electrical) connections, optical andover-the-air connections may also generally be used with systemsaccording to embodiments of the invention. In the case of over-the-airconnections, receivers, transmitters or transceivers may be providedbased on the need to receive information, transmit information, or bothreceive and transmit. For example, force sensor 310 can include anassociated transmitter and antenna, and signal processing system 315 caninclude an antenna and a receiver operable to receive the sensed signaltransmitted by the transmitter associated with the force sensor.

FIG. 3B is a simplified depiction of an exemplary FSW system 350 havinglateral position detection according to an embodiment of the invention.System 350 is operating on workpieces 311 and 312 arranged in a T-jointconfiguration. System 350 comprises FSW tool 305 comprising a spindleactuator 308 having a tool chuck (not shown in FIG. 3B) fixed to arotating shaft thereof for rotational driving of a rotary tool 320comprising shoulder 306 and probe 307. Probe has a length sufficient toextend into workpiece 312. A force sensor 310 is coupled to tool 305. Asignal processing system 315 is coupled to receive force signals fromforce sensor 310. The force sensor 310 shown is affixed to the rotatingshaft of tool 305, and it in turn holds the FSW tool 305. In this way,forces experienced by the FSW tool 305 are transmitted through the toolto the force sensor 310.

As described above, the force sensor 310 can be embodied as a variety ofdifferent load cells to measure one or more forces. The force signalsexperienced by rotary tool 320 transmitted through the FSW tool 305 thatare sensed by force sensor 310 are transmitted to the signal processingsystem 315. As known in the art, the force signals can be filtered,amplified and converted to digital signals. Signal processing system 315can comprise a microprocessor having associated memory, the memoryhaving stored force vs. lateral offset correlation data, such as basedon the data shown in FIGS. 5 and 6 described in the Examples below.

In one embodiment, experiments are performed in the laboratory to gathersufficient data to prepare a general correlation function that relatesthe measured force (or a force related parameter) experienced by thefriction stir tool and the magnitude (and in some embodiments thedirection) of lateral offset. One way of measuring the lateral offset tocompile data for generating a correlation function is to use a stringpotentiometric transducer to directly measure the lateral offset of thestage. The string potentiometer uses a string pull to affect theresistance of a potentiometer, which in turn changes the voltagemeasured by and after signal processing (e.g. analog to digital (A/D)conversion) is translated into a position of the stage. Other methodsfor directly measuring lateral position include, but are not limited to,a magnetic tape reader, or a relative or absolute shaft encoder fixed tothe shaft which moves the stage laterally. Linear position transducersare a general class of transducer which can perform this measurement. Itmay also be possible for simulations to be used instead of experimentsto generate data to compile a correlation function, such as based oncomputational fluid dynamics to simulate the welds or surfacedeformation and the measured forces.

The signal processing system 315 having such data CT a correlationfunction based on such data can determine the lateral offset fromcollected force signals. In one embodiment, the lateral offset can bereported as a real number which represents the lateral position. In thebutt-joint configuration, this measurement is generally in terms of thedistance of the location of probe 307 from the joint line center. Theoffset estimator can be based on a generally non-linear function whichmaps the input forces to an estimated lateral offset. Such a functioncould be derived from a data set through regression, or be implementedthrough a support vector machine, neural network or other suitablemethod. Alternatively, a function can also be derived from models orphysical properties.

As noted above, force sensor 310 measures the magnitude of at least oneforce, such as the axial force experienced by the probe 307 associatedwith tool 305. In the case of T-joints, the force sensor is generallyoperable to detect a force in the range of about 1 kN up to 40 kN forthe axial force. The other forces (in-plane and torque about the axialaxis) during T-joint processing tend to be significantly lower inmagnitude, generally being 100 N to 5 kN. The axial force magnitudealone for certain T-joint configurations has been found to generally besufficient to estimate of the degree (magnitude) of lateral offset, butgenerally not the direction of lateral offset. In order to deduce theside (direction) of the weld an offset is on, in one embodiment forcesensor 310 also measures at least one in-plane force, such as the inplane force along the x-axis shown in FIG. 3B. Alternatively, weavingaccording to an embodiment of the invention described below can be usedto determine the direction.

As briefly described above, weaving comprises the back and forth lateralmotion of the probe and monitoring the sensed force, parameter relatedto force (e.g. vibration) or signal derived therefrom such as thelateral offset signal to determine whether the tool is moving towards oraway from a desired location. In weaving, it is generally assumed thatthe input data is symmetric about the point desired to be maintained. Inthe case where the axial force is maximized at a particular location(alternatively, it could be minimized, or it could be some other force),then the weaving algorithm can move the probe in a weaving pattern,comparing locations relative to each other, and moving towards thelocation of maximal axial force. Weaving can thus be used to identifythe direction to reach a desired lateral location.

For example, if the only signal available is the axial force, in thecase of the T-joint, the relation generally provided would be aninverted parabola centered about the jointline when plotted against themagnitude of the lateral offset (See FIG. 5 described below whichprovides a relation between values of the axial forces (measured inNewtons) for T-joint welds run and the lateral offset (measured ininches). In this case, the FSW tool can be controlled to weave tomaintain maximum axial forces. During the weave, using the sensed axialforce, the tool can move toward the advancing side while the axial forceis sensed to be increasing, and then reverse directions when the axialforce is sensed to begin to decrease. As known in the art, the“retreating side” of a FSW weld joint refers to the transverse side ofthe weld joint where the tangential direction of the rotational motionof the pin is opposite the direction of the advancement of the pinthrough the structural members. The side opposite the retreating side,referred to as the “advancing side” is where the tangential direction ofthe rotational motion of the pin corresponds to the direction of theadvancement of the pin.

The output of the misalignment detection system, such as shown in system300 or system 350, as described above, is generally a real number whichrepresents the lateral position relative to the location of the rotatingmember, such as the probe's location relative to the joint line centerin butt-welding. One additional piece of information that can be helpfulin certain embodiments of the invention is which side of the centerlocation (which provides the maximum force) the FSS tool is offset. Incertain experiments conducted, systems according to embodiments of theinvention have been able to discern this. For example, in the case wherethere are asymmetric forces present (such as demonstrated for thex-force in T-joints; see FIG. 6 described below), then a function,predictor or estimator can generally be configured to predict thelocation of the probe with respect to the desired location, includinginformation about to which side the probe is offset.

However, in certain configurations, information regarding the side ofthe center location may prove difficult to determine. In such cases,weaving as described above can be used to determine which side of thecenter location the rotational tool is on.

Different setups (lap welding, t-joints etc.) and welding parameters(rotation speed, travel speed) are expected to generally impact themagnitude of the recorded sensed force(s) and be accounted for in orderto have an estimation process configured for a specific weld scenario.There are a number of possibilities for offset estimation, includingestimating the absolute amount of the offset and estimating relativelywhether one sensed position is offset by more or less than another andby how much. Because FSS is generally known to have significant processvariation including variations arising from different configurations,welding speeds, tool design and so on, different techniques for offsetestimation may be used for different FSW or FSP scenarios.

Lateral misalignment detection according to embodiments of the inventioncan be used for a variety of purpose in a variety of systems. In oneembodiment, misalignment detection is used to verify that the FSW or FSPtool is properly laterally aligned relative to a selected lateralposition or path referenced to the workpiece(s). This could be used toalert an operator in a conventional system or a robot in a roboticsystem when a misalignment occurs generally more than a predeterminednumerical threshold is detected. Such a misalignment could have seriouseffects on the weld quality.

In another embodiment of the invention, misalignment detection accordingto the invention is used as part of a friction stir system havingadditional components implementing feedback control of the lateralposition of the tool. Such systems are referred to herein as a “throughthe tool tracked FSS”. In such a system, misalignment detection is usedas a feedback signal for a closed-loop lateral position control system.FIG. 4 shows an exemplary friction stir system 400 having through thetool lateral position tracking according to an embodiment of theinvention. Through the tool tracking provides automatic tracking to adesired lateral position (e.g. relative to a joint). Embodiments of theinvention may be particularly helpful for successful joining of “blind Tjoints”, and for robotic welding where tolerances in the robot and thefixturing holding the workpiece(s) provided are generally inadequate toensure proper “tracking” of the joint during processing.

System 400 includes a rotary tool 402 for FSW, a rotational driving unit403 for rotationally driving the rotary tool 402, a press driving unit404 having the rotational driving unit 403 mounted thereon for pressingthe rotary tool 402 against the surface of a welding portion 460 of aworkpiece 450, and a mount bracket 405 for supporting the press drivingunit 404. In addition, the friction stir welding system 400 furtherincludes a force sensor 406 for detecting the force experienced by therotary tool 402 while pressed on the workpiece 450 during operation ofsystem 400.

A control unit 407 comprises a signal processing system 315 forestimating lateral offset and weld controller 420. Control unit 407 isprovided for controlling the lateral position of rotary tool 402 so thatmeasured force falls within a predetermined range based on a detectionsignal from the force sensor 406. The weld controller 420 uses thelateral offset data to control the servo motor 481 which provides powerto robotic arm 485 and optionally servo motor 404A. For example, system400 can be used to actively maintain some lateral position, such as at aseam/joint line in butt-welding. The tracking feature provided by system400 can be particularly helpful when either the actual lateral positionis difficult to obtain accurately through conventional visual means(e.g. for T-joints), or when the joint line is not a straight line, ascan be case in robotic FSW systems, such as system 400 shown in FIG. 4.

The rotary tool 402 is generally made of steel or other material whichis harder than the workpiece 450 and has a grip portion 402A adapted tobe gripped by a chuck, a shank 402B provided on the grip portion 402A insuch manner as to protrude from a distal end face thereof to thereby bepressed against the surface of the welding portion 460 of the workpiece450, and a probe 402C provided on the shank 402B to protrude from adistal end face thereof to be inserted into the welding portion 460. Therotary tool 402 is caused to travel along the line of the weldingportion 460 of the workpiece 450 while being rotationally driven at aspeed of about 100 to 10,000 rpm so that the probe 402C softens thewelding portion 460 by virtue of friction heat to thereby allow theportion being so softened to be plastically deformed in the vicinity ofthe traveling probe 402C. Welding portion 460 is welded when cooled andsolidified.

The rotational driving unit 403 includes the tool chuck 403A forgripping the grip portion 402A of the rotary tool 402 and a spindlemotor 403B having the tool chuck 403A fixed to a rotating shaft thereoffor rotational driving. The spindle motor 403B is mounted on the pressdriving unit 404 at an upper end thereof which is opposite to the toolchuck 403A via a mounting plate 408. In this case, the spindle motor403B is fixed to the mounting plate 408 at the upper end thereof withfasteners such as bolts and nuts while compressibly holding the forcesensor 406 between the mounting plate 408 and itself. In the embodimentshown the sensor 406 is positioned between the tool and the verticalshaft. It is also generally possible for the force sensor to be in anumber of other locations including below the material, elsewhere on theshaft, or even embedded in the tool.

The press driving unit 404 includes a servo motor 404A affixed to themounting bracket 405 with a rotating shaft thereof being orientedupwardly, a ball screw shaft 404B rotatably supported on the mountbracket 405 at upper and lower ends thereof, a belt power transmissionmechanism 404C for constituting a power transmission between an upperend portion of the ball screw shaft 404B and the rotating shaft of theservo motor 404A, a ball screw nut 404D adapted to thread fit on theball screw shaft 404B in such a manner as to be movable vertically, adirect driven bearing rail 404E disposed in parallel with the ball screwshaft 404B and fixed to the mounting bracket 405 at upper and lower endsthereof and a direct driven bearing 404F adapted to fit on the directdriven bearing rail 404E in such a manner as to be movable verticallythere along and integrally coupled to the ball screw nut 404D. Then,fixed to this direct driven bearing 404F is the mounting plate 408 towhich the spindle motor 403B of the rotational driving unit 403 is fixedin turn.

The mounting bracket 405 has a side wall 405A to which the servo motor404A is fixed, and an upper wall 405B and a lower wall 405C on which theball screw shaft 404B and the direct driven bearing rail 404E aresupported at the upper and lower ends thereof, respectively. The upperwall 405B is shown detachably attached (e.g. via bolts and nuts) to arobotic module 480 comprising robotic arm 485 and servo motor 481 formoving the robotic arm 485 and thus the rotational driving unit 403 androtary tool 402 laterally or vertically.

The force sensor 406 outputs a detected force signal to the controller420. The controller 420 is configured to provide a control signal tocontrol the lateral position of rotary tool 402 relative to a joint orother location of the workpiece 450, such as via movement of arm 485based on input signals from the force sensor 406 and a storedcorrelation relation between force and lateral position. Controller canalso control servo motor 404A of the press driving unit 404, such as tochange the rotation speed of rotary tool or the height of the rotarytool.

Controller 420 generally comprises a feedback control unit, a motorcontrol signal output unit and a motor driving circuit. In addition, thecontroller generally includes memory such as Read Only Memory (ROM) forstoring various types of data and programs, such as the force to lateralalignment correlation data or a function therefrom, a Random AccessMemory (RAM) for temporarily storing various types of data and the likeand a Central Processing Unit (CPU) for performing various types ofoperations as well as an input/output interface I/O between the forcesensor 406 controller 420. An A/D converter (not shown) is generallyincluded for converting the analog signal from the force sensor 406 intoa digital signal. The feedback control unit can perform proportional,integral and differential (PID) operations relative to a deviation ofthe actual force relative to a target force to converge the deviationtowards zero.

In one embodiment, through the tool tracking according to an embodimentof the invention enables automatic joint line tracking in FSW. Throughthe tool tracking also enables more complicated weld-seams to beobtained (e.g. a curved weld path). Further the robustness of theprocess can be improved by monitoring the lateral offset even in caseswhere the location of the weld-seam is known, such as by providing anassurance that proper alignment was maintained throughout the weldingoperation. Moreover, a feature of through the tool tracking is that itgenerally does not require added external sensors outside of forcesensors on the tool, which are common in FSW and FSP. This can representa significant savings in both cost and system complexity.

Other operational parameters can change the force sensed by forcesensors according to the invention. However, it is generally possible toseparate out changes in force due to other effects, such as due to achange in pin penetration depth which can change the measured axialforce. In one embodiment of the invention, a two step process isrepeated throughout the welding process. In the first step, the forces(including but not limited to axial force) are used to determine aparticular lateral location relative to a joint, such as center of theweld which provides a maximum axial force. In this case, when the FSWtool is at the weld center, then a load-control function can beperformed. The load control function can comprise changing someparameter (such as the vertical position which changes the pinpenetration depth) to set the axial force to the desired load at thecentered position. This sequence can be repeated throughout the weld.

Although the embodiments of the invention have generally been describedrelative to blind T-joint FSW where the system can detect offset both indirection from the seam and the magnitude of the lateral offset,embodiments of the invention are generally applicable to any type ofweld joint or FSP, and are particularly helpful for automated roboticwelding for FSW or FSP configurations.

Although not described herein, FSW or FSP according to the invention canbe use to join different sample compositions. Moreover, active coolingcan be performed during performing FSW to avoid melting the sample. Forexample, a backing plate (or anvil) which has coolant tubes runningthrough it can be used for cooling.

FIG. 5 shows values of the axial forces (measured in Newtons) for FSWruns with varying amounts of offsets (measured in inches) obtained bythe present Inventors. The welds run in this example were T-joint weldsusing aluminum workpieces. A string potentiometer transducer wasattached to the lateral position to directly measure the lateral offsetof the stage. The function can be seen to be in the shape of an invertedparabola. The maximum force is obtained very near the center of theseam, shown as a lateral offset of nearly zero. More generally, for FSWwelds other than T-joints, the best position for the tool is generallynot at the exact center, but instead is slightly offset toward theadvancing side.

FIG. 6 shows the measured in-plane x-axis forces (measured in Newtons)for FSW runs with varying amounts of offsets (measured in inches)experienced by an FSW tool on the plane of the horizontal member(perpendicular to the axial force) obtained by the present Inventors. Aswith the data shown in FIG. 5, a string potentiometer transducer wasattached to the lateral position to measure the lateral offset of thestage. The function obtained is in a shape characterized by nearconstant force levels at the offset location extremes, with a force ofbetween about −200 and −300 N for lateral offsets between −0.16 to −0.07inches and a force between −600 to −800 N for an offset of between 0.03and 0.16 inches. A transition region between the location extremes has aforce that generally decreases with increasing (more positive) lateraloffset. A force of about −650 N corresponds to a lateral offset ofnearly zero.

The data shown in FIGS. 5 and 6 demonstrates that lateral offsetestimator can be configured by generating a generally non-linearfunction which maps at least one sensed force to a lateral offset. Sucha function could be derived from a data set through regression, or beimplemented through a support vector machine, neural network or othersuitable method. In addition to regression methods, simulations, modelsand physical principles may also generally be used to derive predictivefunctions as well.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. Numerous changes to the disclosedembodiments can be made in accordance with the disclosure herein withoutdeparting from the spirit or scope of the invention. Thus, the breadthand scope of the present invention should not be limited by any of theabove described embodiments. Rather, the scope of the invention shouldbe defined in accordance with the following claims and theirequivalents.

Although the invention has been illustrated and described with respectto one or more implementations, equivalent alterations and modificationswill occur to others skilled in the art upon the reading andunderstanding of this specification and the annexed drawings. Inparticular regard to the various functions performed by the abovedescribed components (assemblies, devices, circuits, systems, etc.), theterms (including a reference to a “means”) used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (e.g., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure which performs thefunction in the herein illustrated exemplary implementations of theinvention. In addition, while a particular feature of the invention mayhave been disclosed with respect to only one of several implementations,such feature may be combined with one or more other features of theother implementations as may be desired and advantageous for any givenor particular application, Furthermore, to the extent that the terms“including”, “includes”, “having”, “has”, “with”, or variants thereofare used in either the detailed description and/or the claims, suchterms are intended to be inclusive in a manner similar to the term“comprising.”

The Abstract of the Disclosure is provided to comply with 37 C.F.R.§1.72(b), requiring an abstract that will allow the reader to quicklyascertain the nature of the technical disclosure. It is submitted withthe understanding that it will not be used to interpret or limit thescope or meaning of the following claims.

1. A friction stir method for processing at least a first workpiece,wherein a system for said method comprises a spindle actuator coupled toa rotary tool comprising a rotating member for contacting and processingsaid first workpiece, comprising: measuring at least one force signal ora parameter related to said force experienced by said rotary tool duringsaid processing, and estimating a lateral position of said rotatingmember relative to a selected lateral position or a selected path,wherein said estimating comprises comparing stored lateral positioncorrelation data or lateral position correlation data based on a storedcorrelation function to said force experienced by said rotary tool todetermine a lateral position of said rotating member with respect to theselected lateral position or the selected path and determining lateraloffset values based on said lateral position; and decreasing a lateraldistance between the rotating member and the selected lateral positionor the selected lateral path based on the lateral offset values.
 2. Themethod of claim 1, wherein said rotating member comprising a shoulderand a probe extending outwardly from said shoulder, whereby said methodcomprises friction stir welding (FSW).
 3. The method of claim 1, whereinsaid method comprises friction stir processing (FSP).
 4. The method ofclaim 1, further comprising the step of weaving to direct said rotarytool in a direction to decrease a lateral distance relative to saidselected lateral position or said selected path.
 5. The method of claim1, wherein said system includes at least one sensor signal enhancementfeature based on said system.
 6. The method of claim 5, wherein saidsystem further comprises a backing plate under said workpiece, whereinsaid sensor signal enhancement feature comprises a material variation ofsaid backing plate, a surface indentation or protrusion in said backingplate, or thickness variation of said backing plate.
 7. The method ofclaim 1, wherein said at least a first workpiece comprises said firstworkpiece and a second workpiece, wherein at least one of said firstworkpiece and said second workpiece includes at least one sensor signalenhancement feature.
 8. The method of claim 1, wherein said methodcomprises welding a blind T-joint.
 9. The method of claim 1, whereinsaid method comprises welding a butt joint.
 10. The method of claim 1,wherein said method comprises welding a lap joint.
 11. The method ofclaim 1, wherein said method comprises the step of controlling a lateralposition of said rotary tool based on said lateral alignment.
 12. Themethod of claim 1, wherein said controlling comprises sending controlsignals to cause a servo motor coupled to a robotic arm to automaticallycontrol said lateral position of said rotary tool so that said sensorsignals are within a predetermined range or said lateral alignment ismaintained within a predetermined limit or range.
 13. The method ofclaim 1, wherein said force comprises an axial force.
 14. The method ofclaim 1, wherein said force comprises an in-plane force.
 15. The methodof claim 1, further comprising the step of issuing an alert to anoperator of said system when said lateral alignment is outside apredetermined limit or range.
 16. A friction stir method for processingat least a first workpiece using a friction stir weld system comprisinga spindle actuator coupled to a rotary tool comprising a rotating memberfor performing said processing, the method comprising: measuring a forceexperienced by said rotary tool or a parameter related to said forceexperienced by said rotary tool during said processing, said force basedon a plurality of force sensor signals associated with said measuredforce or said measured parameter at a plurality of locations on saidfirst workpiece, comparing said plurality of force sensor signals tostored lateral position correlation data or lateral position correlationdata based on a stored correlation function to discern a lateralposition of said rotating member with respect to a selected lateralposition or a selected path, determining at least one lateral alignmentoffset value for said rotating member based at least on said discernedlateral position, and decreasing a lateral distance between said rotarytool and said selected lateral position or said selected path based onsaid lateral alignment offset value.
 17. The method of claim 16, furthercomprising providing a backing plate under said first workpiececomprising a force sensor signal enhancement feature, said force sensorsignal enhancement feature comprising a material variation of saidbacking plate, a surface indentation or protrusion in said backingplate, or thickness variation of said backing plate.
 18. The method ofclaim 16, wherein said adjusting further comprises: moving an arm drivenby a servo motor coupled to said rotary tool arm to automaticallycontrol said lateral position of said rotary tool based on said lateralalignment offset value.
 19. The method of claim 18, wherein said movingfurther comprises moving said rotary tool along said first workpiece ina weaving pattern.
 20. The method of claim 16, wherein said plurality offorce sensor signals are associated with at least one among an axialforce, an in plane force, and a torque experienced by said rotary tool.21. The method of claim 16, further comprising selecting said feature ofsaid first workpiece to comprise at least a portion of said firstworkpiece contacting at least one second workpiece.
 22. The method ofclaim 16, wherein determining is further based on a direction ofrotation of said rotating member.
 23. The method of claim 16, whereinsaid comparing further comprises comparing said plurality of forcesensor signals at consecutive ones of said plurality of locations. 24.The method of claim 16, wherein said determining further comprisesdetermining a direction towards a location of maximal or minimal forcerelative to said current location of said rotating member.
 25. Afriction stir welding method for welding at least a first and a secondworkpiece using a tracked friction stir weld tool comprising a spindleactuator coupled to a rotary tool having a rotating member with ashoulder and a probe extending outwardly from said shoulder forcontacting and processing said first and second workpiece, the methodcomprising: measuring a force experienced by said rotary tool duringsaid processing, said force based on a plurality of force sensor signalsassociated with said measured force at a plurality of locations on saidfirst and second workpiece; comparing said plurality of force sensorsignals to stored lateral position correlation data or lateral positioncorrelation data based on a stored correlation function to discern alateral position of said rotating member with respect to a joint linefor said first and second workpiece; determining lateral alignmentoffset values for said rotating member based at least on said discernedlateral position; and decreasing a lateral distance between saidrotating member and said joint line by adjusting a lateral position ofsaid rotary tool based on said lateral alignment offset values.
 26. Themethod of claim 25, wherein said adjusting further comprises: operatinga servo motor to move an arm coupled to said rotary tool to change saidlateral position of said rotary tool.
 27. The method of claim 25,further comprising: providing a backing plate under at least one of saidfirst and second workpiece, wherein said backing plate comprises a forcesensor signal enhancement feature, said force sensor signal enhancementfeature comprising a material variation of said backing plate, a surfaceindentation or protrusion in said backing plate, or thickness variationof said backing plate.
 28. The method of claim 25, wherein saidadjusting further comprises moving said rotary tool along said firstworkpiece in a weaving pattern.
 29. The method of claim 25, wherein saidplurality of force sensor signals are associated with at least one amongan axial force, an in plane force, and a torque experienced by saidrotary tool.
 30. The method of claim 25, further comprising selectingsaid feature to comprise at least a portion of at least one secondworkpiece contacting said first workpiece.
 31. The method of claim 25,wherein determining is further based on a direction of rotation of saidrotating member.
 32. The method of claim 25, wherein said comparingfurther comprises comparing said plurality of force sensor signals atconsecutive ones of said plurality of locations.
 33. The method of claim25, wherein said determining further comprises determining a directiontowards a location of maximal or minimal force relative to said currentlocation of said rotating member.